1. Field of the Invention
TiB.sub.2 ceramics are hard ceramics, and utilized for cutting tools, plastic working tools, high wear resistance parts and the like. The present invention relates to novel TiB.sub.2 ceramics where the strength and the fracture toughness are improved.
2. Description of the Prior Art
TiB.sub.2 has various characteristics, such as a high melting point, a high hardness and a high wear resistance. Moreover, it is excellent in high temperature corrosion resistance, and is electrically conductive. Therefore, TiB.sub.2 can be processed by electric discharge machining. However, TiB.sub.2 is inferior in flexural strength which is 20 to 30 kgf/mm.sup.2 and in fragile. Thus, various investigations have been conducted in order to improve the strength of TiB.sub.2, and, for example, Japanese Patent No. 1,096,092 discloses improving the flexural strength and fragility by adding nickel boride, cobalt boride, iron boride or the like as binder. Japanese Patent KOKOKU No. 59-7688 discloses improving the strength as well as oxidation resistance and heat resistance by adding a zirconium oxide such as ZrO.sub.2, ZrO, ZrO.sub.0.35 or Zr.sub.3 O.sub.1 -x to TiB.sub.2. Japanese Patent KOKOKU No. 58-57393 discloses that a composite ceramic sintered material having high density, high strength and which is excellent in oxidation resistance is obtained by adding 10 to 60 wt. % of TiB.sub.2 to TiN. Austrian Patent Official Gazette No. 199,886 discloses that composite sintered body of TiC and TiB has high hardness, wear resistance, corrosion resistance and the like.
However, the highest flexural strength of the above sintered bodies is only 110 kgf/mm.sup.2, and the fracture toughness is insufficient. Thus, it has been desired to develop a TiB.sub.2 having a greater strength and fracture toughness in order that TiB.sub.2 can be widely utilized as materials for various uses.